This invention is generally directed to ink compositions, and more specifically the present invention is directed to ink jet inks, such as liquid thermal ink jet compositions. In one embodiment of the present invention, the imaging inks contain as a component any one of the fullerenes, such as buckminsterfullerene, giant fullerenes or mixtures thereof. The aforementioned fullerenes can be selected as the pigment or colorant for the ink, or, for example, as surface additives for other pigments to modify, control and improve their hydrophobic and hydrophilic properties and their adhesion to marking media such as paper or transparencies. Examples of ink jet printing processes, including thermal ink jet, and wherein the inks of the present invention may be selected, are illustrated in U.S. Pat. Nos. 4,601,777; 4,251,824; 4,410,899; 4,412,224; and 4,532,530, the disclosures of which are totally incorporated herein by reference.
Ink jet printing systems can be classified as continuous stream and drop-on-demand. In continuous ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, the system is much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
The other type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability. The inks of the present invention can be selected for the aforementioned systems, especially the thermal ink jet systems in embodiments thereof.
The operating sequence of the bubble jet system is initiated with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be refired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S. Pat. No. 4,412,224, and U.S. Pat. No. 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
Known ink jet inks generally comprise a water soluble dye which is soluble in an ink vehicle such as water or a mixture comprising water and a water soluble or water miscible organic solvent. For example, U.S. Pat. No. 4,184,881 discloses an ink composition for use in ink jet printing comprising an aqueous solution of a water soluble dye and a humectant comprised of ethylene oxide adducts of at least one acetylenic diol in the absence of any glycol or glycol ether. In addition, U.S. Pat. No. 4,337,183 discloses an aqueous printing ink composition which comprises a physical mixture of polyurethane resin, polyethylene resin, and water as the vehicle. Further, U.S. Pat. No. 3,477,862 discloses an ink comprising a dyestuff, a solution of high molecular weight polyethylene oxide and glycerin for employment in a pen, nozzle or other ink applying means to ensure the inscription of a clear continuous solid line on a chart on which the ink applying means is associated as the ink applying means traverses the chart. The disclosures of each of the patents mentioned herein are totally incorporated herein by reference.
Heterophase ink jet inks are also known. For example, U.S. Pat. No. 4,014,833 (Story) discloses a composition and method for improving the ink transfer properties of aqueous printing inks. The composition is an aqueous ink containing from 0.1 to 1.5 percent by weight of a polyethylene oxide resin having a molecular weight in the range of from 100,000 to 350,000. In addition, U.S. Pat. No. 4,680,332 discloses a heterophase ink composition which comprises a water insoluble polymer dispersed in a liquid medium, the polymer containing therein an oil soluble dye, and a nonionic stabilizer permanently attached thereto. The polymer may include styrene, parachlorostyrene, vinyl naphthalene, and acrylates wherein the carbon chain length is from about 1 to about 18 carbon atoms. The stabilizers may include ethylene oxide and propylene oxide block copolymers. Further, U.S. Pat. No. 4,705,567 discloses a heterophase ink jet ink composition which comprises water and a dye covalently attached to a component selected from the group consisting of poly(ethylene glycols) and poly(ethylene imines), which component is complexed with a heteropolyanion. In addition, U.S. Pat. No. 4,597,794 discloses an ink jet recording process which comprises forming droplets of an ink and recording on an image receiving material by using the droplets, wherein the ink is prepared by dispersing fine particles of a pigment into an aqueous dispersion medium containing a polymer having both a hydrophilic and a hydrophobic construction portion. The hydrophilic portion constitutes a polymer of monomers having mainly polymerizable vinyl groups into which hydrophilic portions such as carboxylic acid groups, sulfonic acid groups, sulfate groups, and the like are introduced. Pigment particle size may be from several microns to several hundred microns. The ink compositions disclosed may also include additives such as surfactants, salts, resins, and dyes. The disclosures of each of the patents mentioned herein are totally incorporated herein by reference.
Molecular fullerenes have been described as entirely closed, hollow spheroidal shells of carbon atoms containing 32 to 1,000 or more carbon atoms in each sphere, reference Smalley, R. E. "Supersonic Carbon Cluster Beams in Atomic and Molecular Clusters", Bernstein, E. R., Ed.; Physical and Theoretical Chemistry, Vol. 68, Elsevier Science: New York, 1990; pages 1 to 68, the disclosure of which is totally incorporated herein by reference. The prototypical fullerene, C.sub.60, has been referred to as buckminsterfullerene and has the molecular geometry of a truncated icosahedron, thus the C.sub.60 molecules resemble a molecular sized soccer ball, reference Time Magazine, May 6, 1991, page 66, and Science, vol. 252, Apr. 12, 1991, page 646, the disclosure of which is totally incorporated herein by reference. Molecules of C.sub.60 as well as of C.sub.70 and of other fullerenes have also been referred to as buckyballs. Buckminsterfullerenes are usually comprised of C.sub.60 molecules contaminated with small amounts of C.sub.70 and possibly C.sub.84 molecules or even smaller amounts of higher molecular weight fullerene molecules. The preparation of buckminsterfullerene and of other fullerenes from the contact arc vaporization of graphite and a number of the buckminsterfullerene characteristics such as solubility, crystallinity, color and the like have been described in Kratschmer, W., Lamb, L. D., Fostiropoulos, K., Huffman, D. R., Nature, 1990, Vol. 347, pages 354 to 358, and in Chemical and Engineering News, Oct. 29, 1990, pages 22 to 25, the disclosures of which are totally incorporated herein by reference. The fullerenes are available from Texas Fullerenes Corporation, 2415 Shakespeare Suite 5, Houston, Tex. 77030-1038, Materials & Electrochemical Research (MER) Corporation, 7960 South Kolb Road, Tucson, Ariz. 85706, and Research Materials, Inc., 1667 Cole Boulevard, Golden, Colo. 80401, and are believed to be comprised of mainly C.sub.60 and smaller amounts of C.sub.70 and C.sub.84 carbon molecules, and possibly small amounts of other higher molecular weight fullerenes. Allotropic forms of carbon comprised of spherical assemblies of carbon atoms C.sub.n with, for example, n being the number 60, 70, 84, and the like are considered fullerenes and can be formed as powders by the evaporation of graphite in inert noble gas atmospheres with arcs or lasers, and these fullerenes are available from the sources mentioned herein. The color of the allotrope can depend on the value of n, for example when n is equal to 70 the color is orange, when n is equal to 60 the color is purple magenta, and when n is equal to 62 the color is yellow. It is believed that these new forms of carbon possess a number of advantages for liquid thermal ink jet applications, including, for example, their solubility in organic solvents and, with appropriate chemical modification, such as the attachment of diamine chromophores to the surface of the carbon shell, solubility in water. The other known carbon forms, diamond and graphite and derivatives thereof, are not considered to be soluble in such solvents. Potential advantages of C.sub.60 and the like as pigments over other ink jet pigments include their unusual stability against chemical and physical degradation, together with the unique opportunities they offer for the tailoring of enabling properties such as color hue and density and hydrophilic and hydrophobic character through chemical modification, internal and external of their carbon shell.
Illustrated in copending patent application U.S. Ser. No. 709,734, the disclosure of which is totally incorporated herein by reference, are developer compositions and toner compositions comprised of resin particles, and pigment particles comprised of fullerenes, a new third form of carbon also referred to as buckminsterfullerene or buckyballs, other forms of fullerenes illustrated therein, and other known fullerenes. More specifically, the copending patent application discloses toner compositions comprised of resin particles, and pigment particles comprised of fullerenes, a third form of carbon described as being comprised of 60 atom clusters of carbon arranged at the verticies of a truncated icosahedron and resembling miniature soccer balls. Such a structure resembles the geodesic domes designed by R. Buckminister Fuller, Jr., the namesake of these molecular structures. In one embodiment of the copending application, there are provided toner compositions comprised of resin particles, pigment particles, and fullerenes as charge additives. Also, in another embodiment of the copending application there are provided colored toner compositions comprised of known toner resin particles, fullerene pigment particles, and pigment particles comprised of cyan, magenta, yellow, red, green, blue, brown, or mixtures thereof.
Reference to fullerenes includes all forms of the fullerenes illustrated herein, other known fullerenes, mixtures thereof in embodiments, and the like.